The present invention relates to a method for producing a photosensitive letterpress printing plate used in a letterpress printing such as corrugated board printing, film printing, preprint printing and label printing. In particular, the present invention relates to a method for producing a photosensitive letterpress printing plate which uses aqueous developing liquid, thereby minimizing the waste liquid discharged in a development treatment for a photosensitive letterpress printing plate.
A photosensitive letterpress printing plate has been used as a printing plate for letterpress printing represented by corrugated board printing, film printing, preprint printing and label printing.
APR (trade name, made by Asahi Kasei Corp.), one of the photosensitive resins, is a most typical product as a liquid photosensitive resin, and several models of equipment such as ALF, AWF and ASF (all trade names, made by Asahi Kasei) are commercially available as a plate-making equipment using this photosensitive resin. A plate-making is performed by the following process using the photosensitive resin. Firstly, a photosensitive resin is coated on a transparent carrier film in a uniform thickness, then laminated with a base film. The laminate structure is irradiated by UV light through a transparent image bearer such as a negative film made by another system in advance, through which UV light is selectively transmitted, so that a photosensitive resin in the exposed area photochemically hardens locally to form a relief image, then unhardened resin is removed and recovered using a rubber blade and the like, and finally unhardened resin remaining on a relief surface is washed out completely with wash out solution (developing solution), followed by application of a necessary post-treatment to produce a photosensitive letterpress printing plate to be provided for printing.
In a developing process in which unhardened resin is washed off, presently, unhardened resin is washed off and removed by means of a developing solution having a high chemical activity. However, if the developing solution contains unhardened resin more than a certain amount, the solution loses a developing ability and becomes impossible to be used. The unusable developing solution has to be consigned to an industrial waste disposal trader because the waste solution can not be discharged into sewage or the natural environment. The waste solution is high in volume and disposal cost, and has become an economical problem.
In addition, presently a post-exposure process is carried out after the developing process. This post-exposure process enhances mechanical properties by hardening unreacted resin in and on the surface of the hardened plate obtained in the developing process, and also reduces tackiness on the surface of the hardened plate by irradiating an active light to the printing plate. In this post-exposure process, in order to facilitate a polymerization reaction on the surface of the photosensitive resin layer, a photosensitive resin plate is exposed to active light in a liquid so that the plate is shielded from oxygen in the air. However, practice of the post-exposure process in a liquid results in dirty plate-making equipment and its surroundings and lowering of operation efficiency. Thus, a problem of significant deterioration of the working environment arises.
Based on the above-described situation, development of a method for reducing the cost for treating worn-out developing solution and a method for applying a post-exposure in air to improve the working environment have been strongly demanded.
On the other hand, with regard to a developing process, an example of a developing method, in which a highly pressurized aqueous developing solution is sprayed from spray nozzles to a photosensitive resin layer of an object to be developed, has been disclosed in JP-A-2000-29227 (Kansai New Technology Laboratory Co., Ltd., xe2x80x9cA Pattern Forming Method and Photosensitive Resin Compoundxe2x80x9d). The developing solution used in this developing method is an aqueous developing liquid, substantially water. In a conventional developing method, an unhardened resin is decomposed and removed using the chemical action of a surfactant contained in a developing solution, whereas in this developing method of JP-A-2000-29227, in which unhardened resin is washed off using a developing liquid substantially not containing a chemical component such as surfactant, unhardened resin is scattered and removed by giving large physical energy to a relief surface by means of spraying a developing liquid at high pressure. Accordingly, water can sufficiently work as a developing liquid because the developing liquid does not require chemical activity. Thus the cost for a wash out agent such as surfactant has been reduced, and the life of developing liquid has been extended compared with a developing method using a surfactant because the life of the developing liquid hardly depends on an amount of unhardened resin mixed in the developing liquid, and therefore, the cost to treat waste developing liquid has been reduced. However, although this method could solve the problem to reduce the cost to treat waste developing liquid, it still had a problem that this method could not provide a printing plate having a reproduction on the plate having sharp printing results, as well as that this method required several times the wash out time compared with the conventional method to provide a printing plate having a reproduction on the plate having sharp printing results.
Based on the above described situation, development of a method for developing a photosensitive resin letterpress printing plate is strongly demanded, which makes it possible to reduce the cost to treat worn-out developing liquid, and to give sharp printing results with a comparative developing time to that of the conventional developing method using surfactant.
The invention is directed to respond to these demands, and provides a plate-making method in which the volume of waste developing liquid discharged is reduced by recycling and reusing the developing liquid for a photosensitive resin letterpress printing plate after an exposure process to reduce the cost for treating waste liquid, and at the same time, even a post-exposure process in air can be realized.
The inventors enthusiastically studied to solve the above problems, and found the fact that a photosensitive resin letterpress printing plate with no tackiness on a plate surface can be obtained by removing unhardened resin from the printing plate with physical force using a developing liquid mainly comprising water not containing a special wash out component at a high temperature, then applying a post-exposure in air by adding a small amount of photosensitive hydrogen abstracting agent in the developing agent if necessary, and completed this invention.
Thus, the present invention provides:
(1) A method for developing photosensitive resin letterpress printing plate comprising spraying an aqueous developing liquid at a temperature not lower than 40xc2x0 C. under high pressure to a photosensitive resin letterpress printing plate after exposure.
(2) A method according to the above (1), wherein the aqueous developing liquid is sprayed under a pressure of not lower than 1 MPa and not higher than 30 MPa.
(3) A method according to the above (1) or (2), wherein a gas is mixed in the aqueous developing liquid.
(4) A method according to any one of the above (1) to (3), wherein the aqueous developing liquid is recycled and reused after removing a mixed-in photosensitive resin from the aqueous developing liquid by means of a filter.
(5) A method according to the above (4), wherein a surface of the photosensitive resin letterpress printing plate is sprayed with the aqueous developing liquid, then rinsed with water, and the water is then mixed into the aqueous developing liquid.
(6) A method according to any one of the above (1) to (5), wherein an aqueous developing liquid contains a photosensitive hydrogen abstracting agent.
(7) A method according to the above (6), wherein a surface of the letterpress printing plate is sprayed with the aqueous developing liquid, then irradiated with an active light in air.
(8) A method according to the above (7), wherein the active light is mainly an UV light having a wavelength in a range of 200 to 400 nm.
(9) A method according to any one of the above (1) to (8), wherein at least one nozzle is used to spray the aqueous developing liquid under a pressure of not lower than 1 MPa and not higher than 30 MPa.
(10) A method according to any one of the above (1) to (9), wherein a pump capable of delivering the aqueous developing liquid under a pressure of not lower than 1 MPa and not higher than 30 MPa is used.
(11) A method according to any one of the above (1) to (10), wherein an oil-absorbing mat filter, non-woven fabric filter or paper filter is provided on a surface of the aqueous developing liquid reserved in a tank and/or in a pipe through which the aqueous developing liquid flows, and the aqueous developing liquid is filtered with any of these kinds of filters.
(12) A developing equipment for a photosensitive resin letterpress printing plate used for a method according to any one of the above (1) to (11).
(13) A developing equipment for a photosensitive resin letterpress printing plate comprising:
(a) a plate treatment section comprising a support to fix a photosensitive resin letterpress printing plate and a nozzle header being installed so as to oppose to the support and being arranged with at least one spray nozzle to spray a highly pressurized aqueous developing liquid;
(b) a liquid tank section to reserve the aqueous developing liquid equipped with a heater; and
(c) a high pressure jet pump connected to the liquid tank section in the input side and connected to said nozzle header in the output side.
(14) A developing equipment according to the above (13), wherein the spray nozzle and the high pressure jet pump can spray and deliver the aqueous developing liquid under a pressure of not lower than 1 MPa and not higher than 30 MPa, respectively.
(15) A developing equipment according to the above (13), wherein a filter is installed in said liquid tank section.
(16) A developing equipment according to the above (13), wherein a nozzle header to spray rinsing water is equipped in the plate treatment section, and the liquid tank section is capable of reserving together both rinsing water after spraying and aqueous developing liquid after spraying.
(17) A developing equipment according to the above (13), wherein the plate treatment section further comprises a lamp section arranged with at least one lamp to emit an active light in air.